I searched the world and mostly the DUC for the answer, but could not find it definitively. I have PT11 |HD with HDX and my co-producer-writer is thinking about picking up PT Express and a Fast Track Duo (with PT Express bundled). What we want to do from his side is for him to be able to compose on that system and then send me the tracks he's started and have me open them on my rig and go to work. Not really interested in plug-in compatibility, but need this to open the sessions or at least import them. Then I can finish them on the HD rig. We work long distance.

The FAQ says PT Express can open files (with limitations) from PT11 HD, but no indication if this can happen the other way around). Thanks in advance.
Also, I don't think the Fastrack has MIDI I/O, so how would he record his keyboard?

The other thing to consider is that PT Express only allows 16 audio tracks. He may find this pretty limiting very soon. He will probably want to do the $199 upgrade to regular Protools as soon as possible.